Suspensions for coating and other purposes



Patented May 9, 1939 STAES SUSPENSIONS FOR COATING AND OTHER PURPOSES Victor B. Abrams, East Orange. N. J assignor to Sulflo Corporation of America, a corporation of Georgia 9 Claims.

This invention relates to freely flowing suspensions of finely divided solid particles in organic liquid vehicles, and especially to suspensions of particles of greater than colloidal size. A particular object of the present invention is to provide freely flowing suspensions of pigments for coating purposes, including inks, paints, enamels and lacquers, although the invention is not limited thereto and comprehends other suspensions of 10 solid particles.

Stable, freely flowing suspensions are produced, in accordance with this invention, by distributing through the desired organic liquid vehicle finely divided particles of solvated hydrogenated l castor oil wax having an elastic gel nature. This may be conveniently accomplished, for example, by dissolving a small amount of the wax in the vehicle at an elevated temperature and then cooling to form 'a waxy precipitate, which, upon 20 proper manipulation of the mixture, become broken up into finely divided gel particles distributed through the vehicle, the gel particles being substantially in contact. The resulting mixture will beof free-flowing consistency if a suit- 5 ably small amount of wax has been used.

The particles to be suspended, when distributed through this mixture of vehicle and gelparticles, are prevented'from moving by the gel particles and thus are maintained indefinitely in a stable 30 state of suspension. In other words, thewax is used to efieot a mechanical suspension of the particles without converting the mixture into a semi-solid or non-fiowable state.

As indicated, the function of the solvated wax 35 particles (gel particles) is not to increase the viscosity and thereby slow down the settling or rising of the suspended particles, which would require that the mixture be made of the consistency of a cake or paste to secure reasonable stability as to suspended particles of greater than colloidal size, but is to entrain the suspended particles and mechanically prevent movement thereof without rendering the mixture incapable of free flow. 'The use of the wax in accordance with 45 my invention necessarily somewhat increases the viscosity of the mixture, but this is incidental and does not prevent securing suspension mixtures which may be freely poured and pumped.

50 While suspensions of solid particles of greater than colloidal or sub-microscopic size constitute the most important application of .my invention,

which may be applied to suspensions of particles large enough to be visible to the naked eye, it is 55 evident that particles of colloidal size may likewise be stably suspended in accordance with the invention. Colloidal particles thus suspended are rendered stably suspended not only when in colloidal state but also in the event of agglomeration into particles of greater than colloidal 5 size, which is not true of particles in ordinary colloidal suspensions.

.The gel particles in the suspension mixture are elastic in nature and resist deformation and displacement in a manner such that a small force will merely deflect them without producing continuous motion, and a force in excess of a minimum which depends upon the materials and conditions is required to produce continued motion of any object present in a mass of the particles. The result is that the gel particles, and other particles present, are prevented from moving through the mass, the force of gravity or buoyancy on each particle being less than the minimum force required for continuous motion. In this manner even such dense particles as those of finely divided lead can be prevented from settling out, and finely divided air bubbles can be prevented from rising and escaping.

In order to produce the above effect, the gel particles must be sufliciently close together so that they cannot be merely carried through the liquid vehicle without influencing each other, and this minimum requirement may be readily determined by experiment in any desired case. 0

The wax-vehicle mixture capable oi? sustaining particles in stable suspension may be broadly characterized as a mobile discontinuous gelatinous mass composed of particles of waxy elastic-gel substantially in contact with each other and having the interspaces containing the liquid vehicle, the particles to be suspended being distributed in or between the gel particles and prevented irom moving thereby.

The term gelcosity is used to designate this property of mobile discontinuous gelatinous masses, and thedegree of force required to produce continuous motion without such gel masses. The higher the gelcosity, the greater the force needed to cause continued motion of a particle through the gelatinous mass, and hence the greater the mass of a particle may be without the particle settling out.

The possession of gelcosity and the relative gelcosity of variousv mobile media may be easily determined by using a light metal plate or vane suspended in a vertical plane by a fine wire or fibre secured to a fixed support. The wire should be surrounded by a fixed tube or sleeve to movement or flow within the medium and hence the greater the gelcosity. If the mobile medium is continuous, it can have no gelcosity and the vane will slowly return to the initial position even though the medium is highly viscous; while a medium of high gelcosity will cause a large displacement even though of quite free flowing consistency. In'other words, a displacement of the vane,'whlch measures a static equilibrium condition, is a consequence of the gelcosity and not of the viscosity.

This characteristic of mobile discontinuous gelatinous masses is not possessed by mobile continuous gelatinous masses, that it, gelatinous masses in which no discrete gel particles exist. In the latter case an infinitely small force will produce flow and no gelcosity will be indicated by the above test, just as in the case of non-gelatinous liquid of high or low viscosity. An example of a mobile continuous gelatinous mass is a solution of raw rubber dissolved in a petroleum oil. This possessesthe. characteristics of elasticity, stringiness and may have a high viscosity, but an infinitely small force will produce flow and hence no gelcosity will be exhibited. A gelatinous mass which has set, forming a solid jelly, is also a continuous gelatinous mass, but of course is not mobile and exhibits the overall characteristics of a solid until broken up to form a discontinuous mass, and thus obviously does not possess the characteristics of a mobile discontinuous gelatinous mass containing discrete gel particles.

A representative hydrogenated castor oil wax (produced byhydrogenating castor oil to an extent resulting in a hard waxy product), is milkwhite in color, has a specific gravity of about 0.99 at 20 C., has a melting or solidifying point in the range of about 171-178-F., an acid number of about 2, a saponification number of about 180, and an iodine number of about 3.

The term wax is applied to the hydrogenated castor oil in accordance with technical usage, since this product is of waxy appearance and is generically similar to the so-called natural or true waxes in respect to many properties.

Hydrogenated castor oil wax is relatively insoluble at room temperature and thereabouts in most organic vehicles, and in many cases can be satisfactorily used in-amounts of 1% or less (for example, with mineral oils, petroleum ether, petroleum naphtha, linseed oil, Cellosolve, and others). It appears to approximate universality, as it has been found to be satisfactory when used in amounts of 3% or less with the following liquids selected from commonly known oils and organic solvents: mineral oil, fish oil, castor oil, corn oil, soy bean oil, cotton seed oil, linseed oil (both raw and boiled), tung oil, polymerized tung oil, petroleum naphtha (V. M. 8: P.), petroleum ether, benzene, toluene, xylene, coal tar naphtha, ethyl alcohol (Abs; and methyl alcohol, isobutanol, acetone, amyl acetate, Cellosolve (ethylene glycol monoethyl ether), Methyl Cellosolve (ethylene glycol monomethyl ether),

prevent sway. The vane is placed in the medium tricresyl phosphate, turpentine, carbon tetra.-

chloride and carbon disulfide..

uid thinned, and other modifications and com- 1 binations made use of in preparing the vehicle, as is well known in the art.

The invention contemplates the use of hydrogenated castor oil wax for the purpose described, in combination with all types of liquid vehicles and bases employed in making inks, paints, enamels and lacquers, and which generally comprise a mixture of ingredients. Thus the vehicle may contain bodying and binding agents, such as polymerized tung oil, boiled linseed oil, nitrocellulose, ester gum (a resinuous ester of glycerine and rosin) and other synthetic resinous materials, and natural resinous and gummy products as shellac and copal. A portion of the wax remains dissolved in the vehicle and functions as a plasticizing agent similar to castor oil (which is used in some paints and lacquers, particularly of the nitrocellulose type).

generically characterized as those in which the wax is solvatable or lyophilic, meaning that the liquid is capable of being dissolved in or adsorbed by solid wax particles to render them gelatinous, and in which the wax is relatively insoluble at normal room temperature (20 C. or 68 F.) and thereabouts.

If the wax is readily dissolved in the liquid at an elevated temperature (as distinguished from melting without dissolving), a mutual compatability exists indicating that at lower temperatures solid wax particles will be solvatable (lyophilic) in the liquid. The wax-vehicle combination should be such that it is freely flowing and possessed of substantial gelcosity (suspending power) throughout .at least the temperature range 10-35" C. (50-95 F.).' Hence the wax should .have a solubility-temperature characteristic in the liquid such that no great increase of solubility occurs within the limits of about 10-35 C. (fill-95 F.), as otherwise if sufiicient wax is employed to produce gelcosity at the upper temperatures, there will be so much wax out of solution at lower temperatures that the mixture will not be freely flowing at temperatures to be ex- 10-40" C. (SO-104 F.) and this standard is met and exceeded by all of the various liquid vehicles heretofore named.

The relative insolubility of hydrogenated castor oil wax in a number of common organic liquid vehicles at room temperature and thereabouts,

Solubility of hydrogenated castor oil wax in grams solvent per 100 c. c. of solvent At 18-20 C. -At 33 C.

Since an essentially mechanical suspension of the pigment or other solid particles occurs in the suspending media prepared in accordance with my invention, all types and kinds of pigment and other solid particles may be suspended in vehicles in which they are substantially insoluble and sufiiciently inert, regardless of chemical composition. Thus the invention may be applied generally to obtain stable suspensions of the various pigments in the various organic vehicles employed in the ink, paint and varnish arts, and to obtain new combinations of pigments and vehicles.

As illustrative of various pigments which-may be stably suspended, mention is made of the following: elements and alloys, such as carbon black and metallic aluminum and bronzing powders; oxides, such as zinc white, burnt umber, cobalt blue and red lead; sulfides, such as cadmium yellow and vermillion; hydrates and hydroxides, such as yellow ochre and raw umber; carbonates, such at white lead; silicates, such as terre verte; chromates, such as the yellow chromates (chromates of barium, strontium, zinc and lead), and crome red (basic lead chromate'); various inorganic salts; organic pigments, such as Prussian blue, and the various natural and manufactured lakes, including the dry colors formed by combining dyes with adsorptive or reactive bases such as aluminum hydrate.

Lubricant suspensions may be prepared containing finely divided solid lubricant particles of greater than colloidal size, such as flowers of sulfur and finely divided selenium, tellurium, talc, slaked lime, white lead, white zinc and cork dust.

As further examples of suspensions to which the invention applies, mention is made of grinding, lapping and polishing mixtures containing suspended particles of emery, carborundum, rouge, whiting, or similar substances.

The term solid particles, as used herein includes semi-solid or plastic particles, such as particles or natural and synthetic resins.

The actual preparation of freely flowing suspensions and suspending media will now be described in more detail. All methods involve the essential steps of distributing the wax in the liquid vehicle in the form of finely-divided discrete particles and solvating or gelatinizing the particles. These steps may be performed concurrently or successively; and if performed successively they may take place in either order, that is, the wax may be finely divided and then solvented or gelled, or may be gelled and then the gel mass finely divided. In any case, the initially formed waxy particles may be further subdivided,

or solvated, or both, to secure increased gelcosity,

and this is generally desirable.

In ordinary practice, I use the plan of solvating or gelling the wax with the vehicle of the final product, the wax being either introduced into the whole amount of the vehicle at once, or being first combined with a portion of the vehicle and the remainder then added at an appropriate stage. Alternativel the wax may be gelled with one liquid substance and the gell particles thereafter distributed in another liquid substance. In any case, a concentrated suspension product may be prepared containing more wax then is needed for stably suspending the pigment or other solid particles, and this concentrate may later be diluted by mixing with the same or a different liquid.

The pigment or other solid material, in powdered form, may be introduced at any stage of preparation, that is, it may be mixed with the vehicle before or after the wax is added; and if mixed in after addition of the wax it may be added either before or afterthe wax has been reduced 'to a subdivided gelled state.

It is generally most convenient to incorporate the wax in the vehicle by dissolving the wax in the vehicle at a temperature suflicient for this purpose, and then cooling thesolution, preferably, but not necessarily, without agitation, to a temperature at which most of the wax insoluble at room temperature comes out of solution. The wax may be dissolved in a portion of the vehicle and the remainder (which is at room temperature) then added to facilitate cooling. If

the wax readily forms a gel with the vehicle, a gelatinous phase will be formed, but in some cases a flocculent wax precipitate will be formed which is only partly solvated at this stage.

The next step has as its object the subdivision of the undissolved wax material and the solvation of this material (particularly if it is not already in a highly solvated condition) to form finely divided elastic gel particles distributed throughout the vehicle. This is accomplished by subjecting the .material to thorough mechanical agitation. The mixture maybe agitated by the action of a propeller. type stirrer which is sufficiently vigorous, by being pumped and repumped through a mixing type pump, or by being milled in a ball or pebble mill, in a roll mill, or in a colloidal mill. 4

Pumping treatment may be conveniently performed with a gear pump, for example, having an inlet pipe communicating with the bottom of a tank or other receptacle in which the mixture is placed, and having an outlet pipe discharging above the surface of the mixture in the tank. Increased mechanical action on the mixture may be effected by placing a fine orifice in the discharge pipe line. A spring-loaded check valve serves well, the spring being set so that the fluid mixture pumped therethrough will force the valve disk from its seat to form a ring shaped orifice. The advantage of this type of orifice over an ordinary fixed jet-orifice is that greater uniformity is obtained and clogging is avoided. When material is deposited on the valve seat and disk, the disk will automatically move away from the seat so as to maintain the orifice and permit the deposited material to be washed away.

It is generally preferable to mix the pigment or other material to be suspended, in powdered form, with the wax-vehicle mixture before the latter is subjected to mechanical treatment, or during the course of such treatment, in order to distribute the pigment or other particles uniformly throughout the mixture at the same .time that the finely divided gel particles are being formedand distributed. The mechanical treatment in the presence of the wax material assists in breaking up and deagglomerating the pigment or material, and at the same time the pigment or other particles increase the mechanical action on the wax particles and facilitate their subdivision'and solution. Grinding of pigment material in the vehicle of the product is often resorted to, and such grinding may be performed following incorporation of wax in accordance with the present invention, the grinding simultaneously subjecting the wax to the desiredmechanical action.

Mechanical working of a severe nature is generally required to cause adequate solvation of wax in vehicles of the non-viscous organic solvent type, such as petroleum ether, naphtha, benzene, toluene, turpentine, alcohol, acetone, Cellosolve, carbon tetrachloride, and the like. With respect to incorporation of wax in these vehicles, it is'not enough to merely subdivide the wax material, and mechanical work is needed to cause the liquid to solvate the solid wax phase so as to obtain elastic gel particles. When viscous oil vehicles are used, the wax will usually gel satisfactorily with the vehicle without agitation, that is, a gel willbe formed merely by cooling the initial hot solution of wax in oil, and a mere stirring will produce a mixture which possesses gelcosity; although agitation should be used in order to subdivide the gel into fine particles. When a non-viscous vehicle is employed, cooling of the initial solution will generally result in a flocculent wax precipitate and the mixture will not ex hibit substantial gelcosity upon mere stirring,-

severe mechanical working being needed to cause liquid to dissolve in or be adsorbed by the wax particles.

A small amount of a wetting agent may be added to facilitate subdivision of the wax or gel particles during mechanical working, Subdivision of the particles produces an increase in the total-surface area of the particles, resulting in an increase in the interfacial or surface energy of the particle system. The greater the magnitude of this energy the greater the resistance to further subdivision, and the greater the tendency of the particles to agglomerate in order to decrease the surface area and surface energy. Under any given working conditions, for example with a particular pumping set up, the available kinetic energy acting on the individual particles is able to reduce the particle size to a meteor les definite value only, and no smaller, the energy required for further subdivision being greater than that available. By using a wetting agent, which is adsorbed by the particles, the surface energy per unit of surface area is made lower than it would be otherwise, and hence a greater subdivision and smaller particle size will be produced. Sulphonated castor oil (Turkey Red oil) is an example of a suitable wetting agent and is effective when added to the wax vehicle mixture in amounts of a fraction of one percent. The wetting'agent will also act as an agglomeration inhibitor for the wax particles, and may serve the same functions with respect to the pigment or other suspended particles. Other examples of suitable wetting agents are those sold under the trade-names of Erkalin and Avirol.

The smaller the size of the gel particles, the greater the suspending power (gelcosity) of the medium, and hence the smaller the amount ofwax needed.

Unless sufilcient gel material is present to exist in equilibrium with the liquid phase, a. serum layer will form even without the presence of pigment or other suspended solid particles in the gelatinous mass. This may be caused by an insufficient concentration of gel particles, due to insufficient wax having been incorporated, resulting in a settling of the gelparticles until in substantial contact, the mass of gel particles being surmounted by a serum layer of the liquid. If the wax patricles are of lower specific gravity than the vehicle, the serum layer will form on the bottom of the container.

Even when substantially in contact, the individual gel particles will tend to contract, with a resultant bleeding out of liquid contained therein, until an equilibrium is established, if they have originally taken up too much liquid; this effect being known as syneresis; This may be avoided by employing a greater amount of wax.

The presence of entrained pigment or other particles of greater density will result in compression of a. mass of gel particles, with the result that a portion of the liquid present in and between the gel particles may be squeezed out and rise to the surface as a serum layer. This may be avoided by employing a suflicient amount of wax, but the formation of a serum layer is not necessarily detrimental. That is, the formation of a serum layer does not'mean that the pigment or other particles are not stably entrainedand suspended in the mass of gel particles, but it indicates that an excess of liquid is present. There is no settling of the pigment or other particles to a cake or compact layer on the bottom of thereceptacle, as the pigment or other particles will be stably suspended in the mass of gel particles assuming that this mass possesses adequate gelcosity) Gentle agitation or stirring will cause the serum layer to redistribute itself throughout the gelatinous mass to reform a completely uniform mixture. r

The tendency to form a serum layer will be counteracted by finely divided air bubbles which become entrained during extended pumping or other mechanical agitation of the suspension durin preparation. Such dispersed air globules of small size will be held within the gelatinous mass 5 and will be mechanically prevented from rising and escaping just as the solid suspended particles are prevented from settling, the force of buoyancy on the air particles being insuflicient to produce movement, owing to the gelcosity effect. The buoyant force of the air bubbles tends to offset the downward drag of the suspended solid particles and reduces the compression exerted by the latter, thus reducing the tendencyto form a seruni layer. This effect may be further increased, to minimize any serum layer, by so con--. ducting the agitation of the mixture as to favor the entrainment of air. For example, a pumping arrangement as hereinbefore described, in which the mixture is discharged from the circulating pump in a stream onto the surface of the main body, .will cause splashing favoring the entrainment of air, and the pumping will tend to finely 'divide the bubbles thus incorporated. Air may also be forced into the pipe line and thus introduced, and this will be particularly eifective when the mixture is forced through a line orifice. This use of air for the minimization of serum layers is described in more detail in the patent to V. R.

Abrams, No. 2,007,137, issued July 2, 1935, to which reference may be made.

The use of wax, in pigment-containing suspensions such as inks and paints, in accordance with this invention, results in products having improved tinctorial value, and a smaller percentage of pigment can be used.

The presence of the wax gel particles has a still further advantage in the case of inks used in intaglio or gravure printing. In such printing, the ink is applied over the whole printing plate and the surplus then wiped off with a doctor blade. The gel particles exert a lubricating action which substantially reduces the Wear on the printing plate and on the doctor blade. This advantage is particularly important with respect to large runs on rotary presses. The steel doctor blade bears against an etched copper cylinder, causing the pigment in the ink to exert a marked grinding eilect and substantial wear is produced in this way, both on the cylinder and on the blade. Reduction of wear owing to the lubricating action of the gel particles, not only increases the life of the doctor blade, but of vastly more importance, increases the number of copies that can be printed from a cylinder "and makes possible the use of fewer cylinders in big runs. When a cylinder becomesworn, it is necessary to stop the press and replace it, and a reduction in the number of such changes not only reduces the cylinder costs but the loss of time and the labor and other costs which arise from each change-over.

The three principal types of thin pigmented printer's inks are: intaglio or gravure inks; aniline type inks containing pigments to give opacity, for printing or Cellophane and other transparent sheets; and news inks. Employment of the invention in the printers ink art is of particular importance with respect to these three types of inks.

In the following examples specific representative embodiments of the invention are set forth for purposes of illustration.

Example 1 Printers ink of the intaglio or gravure type may be prepared having a vehicle composed of a volatile hydrocarbon, such as benzol (for fast drying inks) or V. M. & P. naphtha (for slow drying inks), blended with a bodying and binding component of ester gum or varnish gum amounting to about one-third of the vehicle, and containing 20-25% by weight of pigment. About 13% by weight of hydrogenated castor oil wax, relative to the vehicle, is added to the vehicle and dissolved therein by heating together. The mixture is allowed to cool and the pigment (such as car bon black or a dry color) is added, the re sulting ink mixture then being thoroughly agitated by pumping or milling (as in a pebble mill) until a smooth uniform product is obtained.

Example 2 Printers inks of the aniline type may be prepared using as the vehicle a mixture of about two parts by weight of ethyl alcohol (95%) and one part of shellac. The vehicle mixture is heated and about 1-2% of hydrogenated castor oil wax is dissolved therein. The mixture is cooled and the pigment added (such as carbon black or a dry color) to make about 20-35% by weight. The resultant mixture is then agitated, as by pumping or milling until smooth and uniform.

Example 3 News may be prepared in the same man,- ner. A non-volatile mineral oil, such as cordage oil (a petroleum paraflin oil having a Saybolt viscosity of about 60 at 100 F.) with or without a gum binder, is used as the vehicle, and a suitable wax is incorporated therein as indicated in the preceding examples. About 12-48% of car-' bon black (0r a colored pigment) is then added and the mixture agitated until smooth and uniform.

Example 4 An aluminum paint of excellent quality may be prepared having a vehicle comprised of 32 parts by weight of ester gum dissolved in 50 parts of V. M. & P. naphtha, in which 1 part of hydrogenated castor oil wax is dissolved by heating together. The mixture is allowed to cool and 1'7 parts of aluminum paint powder are added, the resulting mixture then being thoroughly agitated until a smooth uniform product is obtained.

This paint does not cake in the can and can be readily applied with a brush. A feature is that it forms a satin or matte finish when painted on a cold surface and allowed to dry, and a large part of the matte effect is retained even when heat is applied after drying. When painted on a hot surface, full gloss is obtained due to the leafing of the aluminum flakes as with an ordinary unstabilized aluminum paint.

This application is in part a continuation of my copending application Ser. No. 751,413, filed November 3, 1034, and is a division of my application Ser. No. 84,589, filed June 10, 1936.

In the claims the word solvated is used in its usual sense, meaning compounded with a liquid to form a gel-like substance, similar to hydrated particles where water is the liquid.

I claim the following as my invention:

1. A freely flowing pigment suspension for coating purposes comprising an organic liquid alkyl hydroxide, in which hydrogenated castor oil wax is lyophilic and relatively insoluble at temperatures below 40 (3., containing finely divided pigment particles of greater than colloidal size and finely divided particles of hydrogenated castor oil wax solvated by the vehicle and present in suflicient amount to stably suspend said pigment particles without preventing free flow.

2. A freely flowing suspension comprising an organic liquid alkyl hydroxide, in which hydrogenated castor oil wax is lyophilic and relatively insoluble at temperatures below 40 C., containing finely divided solid particles of greater than colloidal size and finely divided particles of hydrogenated castor oil wax solvated by the vehicle and present in suificient amount to stably suspend said solid particles without preventing free flow.

3. A freely flowing pigment suspension for coating purposes comprising a volatile liquid of the alcohol group having finely divided gel particles of hydrogenated castor oil wax and finely divided pigment particles distributed therethrough and suspended by said gel particles, the wax being solvated by said liquid and in amount sufficient to stably suspend said pigment particles without preventing free flow.

'4. A freely flowing suspension comprising a amount suflicient to stably suspend said solid particles without preventing free flow.

5. A freely flowing pigment suspension for coating purposes comprising alcohol containin finely divided pigment particles distributed therethrough, and finely divided particles of hydrogenated castor oil wax solvated by the alcohol distributed therethrough in sufiicient amount to aroused temperatur in amount suflicient to stably suspend said. pigment particles.

8. A fiowable pigment suspension for coating purposes comprising a solvent of the alcohol group mixed with a substance of the class consisting of natural and synthetic resins and pigment particles, and containing finely divided solvated hydrogenated castor oil wax particles relatively insoluble in said suspension at room temperature in sufficient amount to form a discontinuous gel wherein said pigment particles arestably suspended.

9. A fiowable suspension comprising a solvent of the alcohol group mixed with a substance of the class consisting of natural and synthetic resins and solid particles, and containing finely divided solvated hydrogenated castor oil particles relatively insoluble in said suspension at room temperature in suflicient amount to form a. discontinuous gel wherein said solid particles are stably suspended.

VICTOR R. ABRAMS. 

